U.S. patent application number 13/202888 was filed with the patent office on 2012-02-16 for loudspeakers.
This patent application is currently assigned to HiWave Technologies (UK) Limited. Invention is credited to Christien Ellis.
Application Number | 20120039494 13/202888 |
Document ID | / |
Family ID | 40565565 |
Filed Date | 2012-02-16 |
United States Patent
Application |
20120039494 |
Kind Code |
A1 |
Ellis; Christien |
February 16, 2012 |
Loudspeakers
Abstract
The invention relates to a drive unit for a loudspeaker, and a
loudspeaker including the same. The drive unit includes a magnet
assembly which defines primary and secondary gaps with respect to
which a voice coil assembly is movable and in which the same is
mounted. The voice coil assembly includes a former which is located
and suspended in the secondary gap by ferrofluid provided in said
secondary gap, to locate the voice coil assembly without the need
for a spider or other mechanical locating means to be provided.
Inventors: |
Ellis; Christien;
(Hertfordshire, GB) |
Assignee: |
HiWave Technologies (UK)
Limited
Cambourne, Cambridgeshire
GB
|
Family ID: |
40565565 |
Appl. No.: |
13/202888 |
Filed: |
February 16, 2010 |
PCT Filed: |
February 16, 2010 |
PCT NO: |
PCT/GB2010/000271 |
371 Date: |
November 1, 2011 |
Current U.S.
Class: |
381/166 |
Current CPC
Class: |
H04R 9/027 20130101;
H04R 9/041 20130101; H04R 2440/07 20130101 |
Class at
Publication: |
381/166 |
International
Class: |
H04R 1/00 20060101
H04R001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 2009 |
GB |
0903033.9 |
Claims
1. A loudspeaker drive unit including a moving coil motor including
a magnet assembly with primary and secondary gaps defined thereby,
a voice coil assembly axially movable with respect to said primary
and secondary gaps, said voice coil assembly including a former and
an electromagnetic coil mounted on the former at the location of
the primary gap and wherein the former is positioned with respect
to the secondary gap by the influence of ferrofluid located in said
secondary gap.
2. A drive unit according to claim 1 wherein the voice coil
assembly is solely located by the influence of the ferrofluid in
the secondary gap.
3. A drive unit according to claim 1 wherein ferrofluid is provided
in the primary gap.
4. A loudspeaker drive unit according to claim 1 capable of a
substantially full range of operation.
5. A loudspeaker drive unit according to claim 4 adapted to operate
in piston mode at low frequencies and in bending wave mode at high
frequencies.
6. A loudspeaker drive unit according to claim 1 wherein the drive
unit includes a small diaphragm.
7. A loudspeaker drive unit according to claim 6 wherein the
diaphragm of the drive unit is substantially flat.
8. A loudspeaker drive unit according to claim 1 wherein the unit
has a diaphragm with an aspect ratio of at least 4:1.
9. A loudspeaker drive unit according to claim 1 wherein a
plurality of voice coil assemblies are provided to drive a
diaphragm of the drive unit.
10. A loudspeaker drive unit according to claim 9 wherein the voice
coil assemblies are spaced apart along the length of an elongate
shaped diaphragm.
11. A loudspeaker drive unit according to claim 1 wherein the unit
is adapted to generate bass frequencies.
12. A loudspeaker drive unit according to claim 1 wherein the
former is tubular in shape.
13. A drive unit according to claim 1 wherein the drive unit
includes a substantially circular diaphragm with a maximum diameter
of less than 152.4 mm.
14. A drive unit according to claim 1 wherein the drive unit
includes a diaphragm which is elongate in shape and has a maximum
width of less than 127 mm.
15. A drive unit according to claim 1 wherein the moving coil motor
is a high excursion moving coil motor.
16. A drive unit according to claim 1 wherein a first end of the
former is located to drive a diaphragm of the drive unit, and the
voice coil is located towards the second end of the former, with at
least part of the portion of the former between the voice coil and
the said first end located in the said secondary gap.
17. A drive unit according to claim 1 wherein the position of the
former with respect to the side walls of the secondary gap is
influenced by the ferrofluid present in the secondary gap.
18. A drive unit according to claim 17 wherein the spacing of the
former from the side walls of the secondary gap is maintained
substantially constant by the influence of the ferro fluid.
19. A drive unit according to claim 17 wherein the former is
substantially centrally positioned in the secondary gap by the
influence of the ferrofluid.
20. A loudspeaker drive unit having a diaphragm and a moving coil
motor having a magnet assembly with a primary gap region and a
secondary gap region, and a voice coil assembly arranged for axial
movement in the said gaps, the voice coil assembly including a
former and an electromagnetic coil wound on the former such that
the coil is located in or adjacent to the primary gap and another
portion of the former is disposed in the secondary gap and wherein
ferrofluid is provided in at least the secondary gap to act to
suspend the former and hence the voice coil assembly in a
substantially constant position with respect to the spacing from
the side walls of said gaps while allowing axial movement of the
voice coil assembly with respect to the magnet assembly to drive
the diaphragm.
21. A loudspeaker drive unit having a small diaphragm,
characterised by a high excursion moving coil motor having a magnet
assembly defining a gap having a primary gap region and a secondary
gap region, and a voice coil assembly arranged for axial movement
in the gap, the voice coil assembly comprising a tubular former
having opposed first and second axial ends, said first end portion
adapted to be drivingly coupled to the loudspeaker diaphragm, an
electromagnetic coil wound on the former near to the second end of
the former, and an intermediate portion disposed between the coil
and the first end of the former, the arrangement being such that
the coil is located in the gap adjacent to the primary region and
that the intermediate portion of the former is disposed in the gap
adjacent to the secondary region, and characterised by ferrofluid
provided in at least the secondary gap which acts to suspend the
former in the gap for axial movement therein.
22. A loudspeaker including a baffle and a loudspeaker drive unit
as claimed in claim 1 mounted on the baffle.
Description
[0001] The invention relates to improvements to Loudspeakers, in
particular to the moving coil assemblies provided, and more
particularly, but not exclusively, to moving coil motors such as
those which are used to drive the diaphragms of loudspeaker drive
units, and to drive units and loudspeakers incorporating such
moving coil assemblies.
[0002] As is known, such moving coil assemblies include a magnet
assembly which defines an annular gap and a coil assembly is
arranged in the annular gap so as to be axially and reciprocally
movable therein in response to an alternating electrical signal
which is applied to the coil assembly. Such coil assemblies are
commonly known as "voice coils".
[0003] A form of drive unit known as excursion pistonic diaphragm
loudspeaker drive units, e.g. cone-type loudspeaker drive units,
normally comprise a chassis which supports the magnet assembly of
the motor and a conical diaphragm, which is drivingly coupled to
the coil assembly. The conical diaphragm is usually supported on
two flexible suspension elements to ensure that it moves in a
linear fashion. These are known as the "surround" and the "spider"
respectively, the surround being attached between the outer
periphery of the diaphragm and the chassis and the spider being
attached between the inner periphery of the diaphragm and the
chassis. Since the inner periphery of the diaphragm is coupled to
the voice coil, the spider can alternatively be connected between
the voice coil former and the chassis. The two suspension elements
are normally spaced apart axially as far as is possible to increase
the stability of the coil assembly in the annular gap. For large
excursions, both the surround and the spider are required to extend
linearly over the majority of the maximum excursion of the driver.
Typically large roll-surrounds and large diameter spiders are
generally employed to achieve this in larger drive units. Smaller
size excursion drive units, e.g. so-called tweeters, often use a
single suspension element for the diaphragm and voice coil. This
single suspension can be formed by a continuation of the outer
periphery of the diaphragm material as one or more corrugations.
This is typically done in dome-shaped drive units.
[0004] However, problems are experienced in the design of small,
high excursion drivers due to the lack of available space in the
unit in which to accommodate the suspension. The inclusion of a
spider design presents an even more difficult problem because of
the lack of space. In these smaller drive units, large excursion
spiders cannot be accommodated, and as a result, the linearity and
excursion of the drive unit is often compromised. However,
conventionally removal of the spider altogether is not practically
possible, even if it is possible to achieve static centration of
the voice coil. This is due to the possibility of rocking modes in
the diaphragm in the operating bandwidth of the drive unit which
cause instability of the voice coil in the gap of the magnet
assembly.
[0005] It is has been previously proposed to use a single
suspension full range loudspeaker drive unit having a rectangular
high aspect-ratio flat diaphragm, with the diaphragm operating both
in piston mode and in bending and with a single centrally placed
exciter. Such a design, using only a surround suspension and no
spider suspension, requires a relatively large voice coil gap in
the magnet assembly to accommodate the lateral displacement of the
voice coil in use due to rocking modes in the diaphragm. Thus the
motor efficiency is compromised in the interests of
reliability.
[0006] In United States patent application publication
US2007/0189572 A1 there is disclosed a musical instrument
loudspeaker system comprising; a cabinet; at least a planar
magnetic driver for mid and high frequency sound signals mounted in
the cabinet; and at least one conical voice coil driver for low
frequency mounted in the cabinet. In this case the conical voice
coil driver comprises; a voice coil; a magnet; a cone; and a
ferrofluid interposed between said voice coil and said magnet, said
ferrofluid constituting an alignment means for aligning said voice
coil with said magnet.
[0007] However, there are significant problems associated with the
use of ferrofluid in the gaps of high excursion moving coil systems
of large loudspeaker drive units, not least due to the tendency of
droplets of the ferrofluid to be flung from the gap during
operation of the drive unit. It is believed that this may arise as
a result of drag or turbulence caused by motion of the coil in
operation. To mitigate the loss of ferrofluid during use it has
been proposed that a so-called "bucking" magnet be positioned to
catch droplets of ferrofluid sprayed from the gap.
[0008] An object of the invention is to address the problem of
providing a suspension system which ensures that the voice coil is
accurately positioned and particularly, although not necessarily
exclusively, to provide a system which is suitable for
implementation in high excursion relatively small (as hereinafter
defined) loudspeaker drive units.
[0009] In a first aspect of the invention there is provided a
loudspeaker drive unit including a moving coil motor including a
magnet assembly with primary and secondary gaps defined thereby, a
voice coil assembly axially movable with respect to said primary
and secondary gaps, said voice coil assembly including a former and
an electromagnetic coil mounted on the former at the location of
the primary gap and wherein the former is positioned with respect
to the secondary gap by the influence of ferrofluid located in said
secondary gap.
[0010] According to the invention in a further aspect, there is
provided a high excursion moving coil loudspeaker drive unit having
a small diaphragm, characterised by a magnet assembly defining a
gap having a primary gap region and a secondary gap region, a voice
coil assembly arranged for axial movement in the gap, the voice
coil comprising a tubular former having opposed first and second
axial ends and having a first end portion adapted to be drivingly
coupled to a loudspeaker diaphragm, an electromagnetic coil wound
on the former near to the second end of the former, the arrangement
being such that the coil is located in the gap adjacent to the
primary region and that the intermediate portion of the former is
disposed in the gap adjacent to the secondary region, and
characterised by ferrofluid in the secondary gap and suspending the
former in the gap for axial movement therein.
[0011] In a yet further aspect of the invention there is provided
loudspeaker drive unit having a small diaphragm, characterised by a
high excursion moving coil motor having a magnet assembly defining
a gap having a primary gap region and a secondary gap region, and a
voice coil assembly arranged for axial movement in the gap, the
voice coil assembly comprising a tubular former having opposed
first and second axial ends, said first end portion adapted to be
drivingly coupled to the loudspeaker diaphragm, an electromagnetic
coil wound on the former near to the second end of the former, and
an intermediate portion disposed between the coil and the first end
of the former, the arrangement being such that the coil is located
in the gap adjacent to the primary region and that the intermediate
portion of the former is disposed in the gap adjacent to the
secondary region, and characterised by ferrofluid provided in at
least the secondary gap which acts to suspend the former in the gap
for axial movement therein.
[0012] A small diaphragm loudspeaker drive unit in the context of
the present application is one in which, in the case of a circular
diaphragm, has a maximum diameter of not substantially more than
152.4 mm and is preferably no more than 127 mm in diameter. In the
case of an elliptical or rectangular diaphragm, a small drive unit
is one have a maximum width of not substantially more than 127
mm.
[0013] It is conventional for the voice coil assembly to comprise a
former that is circular in cross-section, and in this case the gap
in the magnet assembly is annular in shape. It is however possible
to make the voice coil former to be of other cross-sectional
shapes, e.g. of so-called "race track" shape that comprises a
parallel pair of straight portions joined together by semi-circular
portions.
[0014] Ferrofluid may also be present in the primary gap.
[0015] The drive unit may be intended for full range operation and
may operate in piston mode at low frequencies and in bending wave
mode at high frequencies. Alternatively, the drive unit may be
intended for bass frequencies only.
[0016] The diaphragm may be circular or may be elliptical or
substantially rectangular in shape. The diaphragm may be of high
aspect ratio. The diaphragm may be conical or otherwise dished or
flat.
[0017] The invention is diagrammatically illustrated, by way of
example, in the accompanying drawings, in which:
[0018] FIG. 1 illustrates schematically an embodiment of the
invention;
[0019] FIG. 2 is a cross-sectional side view of a loudspeaker drive
unit; in accordance with one embodiment of the invention;
[0020] FIG. 3 is a cross-sectional side view of a further
embodiment of a loudspeaker drive unit, in accordance with the
invention;
[0021] FIG. 4 is a cross-sectional side view of a loudspeaker
incorporating the drive unit of FIG. 3.
[0022] Referring firstly to FIG. 1 there is illustrated,
schematically, the features of the invention in accordance with one
embodiment. The drive unit 20 includes a diaphragm 2 connected to
be driven by a voice coil assembly 19 mounted to be axially
movable, as indicated by arrow 31, with respect to a magnet
assembly or system 15. The magnet assembly defines a primary gap 11
and a secondary gap 33.
[0023] The voice coil assembly 19 includes a former 5 which has an
end 35 connected to drive the diaphragm 2 and an opposing end 37.
Towards the end 37 there is mounted the voice coil 4 and this is
located in the primary gap 11. A further portion 39 of the former
19 is located in the secondary gap 33 and is located with respect
to the side walls 41 of the gap by the provision of ferrofluid 43
which acts to maintain the former in a substantially constant
spaced position from the side walls 41 while ensuring the axial
movement 31 of the former 5 can be performed.
[0024] Referring now to FIG. 2 of the drawings, there is shown a
loudspeaker drive unit 20 made in accordance with the present
invention and comprising a chassis or basket 3 which rigidly
supports a magnet system 15 comprising a generally tubular cup 12
having one closed end 16 and in which is rigidly mounted a
concentric stack formed by a disc-like magnet 9, a disc-like
primary or inner pole piece 10, a secondary disc-like magnet 7 and
a secondary or outer disc-like pole piece 8. The primary magnet 9
and secondary magnet 7 are both axially magnetised and are arranged
with their fields in opposition. The stack of magnets 7,9 and the
pole pieces 8,10 are positioned concentrically in the cup 12 and
are of smaller diameter than the interior of the cup to form a
small annular gap 17 between the interior curved wall of the cup
and the magnet/pole piece stack.
[0025] The chassis 3 resiliently supports a conical loudspeaker
diaphragm 2 at its outer periphery by means of a flexible roll
surround 1 to permit the diaphragm to move axially. The inner
periphery of the conical diaphragm is closed by a concentric dome
which thus forms part of the radiating surface of the
diaphragm.
[0026] A voice coil assembly 19 comprising a tubular former 5 on
which is wound a coil 4 is mounted in the gap 17 so as to be
axially reciprocal therein and with its coil 4 opposite to the
primary pole piece 10. One end of the coil former 5 is fixed to the
diaphragm so that it drives the diaphragm in response to an
alternating electrical signal fed to the coil.
[0027] A second suspension is formed by filling an intermediate
portion 6 of the annular gap adjacent to the secondary pole piece
with ferrofluid so that the voice coil former is smoothly guided in
the annular gap. This portion of the gap can be referred-to as the
secondary gap, as distinct from the primary gap 11 in the vicinity
of the coil 4.
[0028] In FIG. 3 there is shown a second embodiment of loudspeaker
drive unit in accordance with the invention. In this embodiment,
the drive unit is very similar to that shown in FIG. 2 with the
exception that here the diaphragm 13 is flat. FIG. 4 shows a
loudspeaker drive unit of the kind shown in FIG. 3 mounted in a
box-like enclosure 14 to form a loudspeaker.
[0029] Advantages of the embodiments of loudspeaker drive unit
motor described above with reference to the drawings, include that
the absence of the spider coupling to the diaphragm results in
improved frequency response smoothness and a reduced moving mass.
This can be beneficial when used in the full range drive units.
[0030] An improved sound quality can be achieved due to better
acoustic flow from the rear of the driver. High linearity can also
be achieved thus allowing high excursions and high efficiency due
to the dual gap motor which is created. Good voice coil lateral
(x,y) stability is achieved as well as a reduced tendency for
ferrofluid to be lost from the secondary gap as it is located away
from the turbulence caused by the movement of the voice coil in the
primary gap. A longer life can thus be achieved for the ferrofluid
in the secondary gap due to its location away from the turbulence
and also its spacing from the heat generated by the coil. In terms
of the audio which is generated improved performance is achieved
especially with respect to bass performance of small area, low
footprint drive units in particular, and high excursion capability
is achieved for drive unit applications in limited space, such as
in TV, multimedia and automotive applications.
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